The present invention generally relates to a boom-type vehicle, such as an extendible boom forklift, as is commonly used in construction, industrial, maintenance and repair applications. More particularly, the present invention relates to a control system for such reach-type vehicle that is adapted for use in combination with a personnel work platform (PWP) that can be used in combination with the reach-type vehicle.
Presently, extendible boom forklifts can be used with a separate personnel work platform such that the forklift can be used to raise and lower workers standing on the platform based on various workplace requirements. The personnel work platform typically includes a pair of tubular fork receivers that receive the forks of the forklift such that the personnel work platform is supported on the forks of the forklift. Typically, an operator sits in the cab of the extendible boom forklift and raises and lowers the personnel work platform into the desired location. Thus, the combination of the personnel work platform and the extendible boom forklift increase the number of functions the extendible boom forklift can perform at a workplace.
Although the combination of the extendible boom forklift and the personnel work platform increase the utility of the extendible boom forklift, the workers supported by the personnel work platform can be injured if the control functions of the extendible boom forklift are not modified when the personnel work platform is being used. For example, if workers are on the platform and the forklift is allowed to move or the fork assembly is allowed to rotate, or the forklift frame is not leveled correctly, the workers could become injured as a result of such movement.
Therefore, it is an object of the present invention to provide a control system for an extendible boom forklift or similar boom-type vehicle that limits the operation of the vehicle when the personnel work platform is being used. Further, it is an object of the present invention to provide relatively slow movement of the frame leveling cylinder when the personnel work platform is in use. A still further object of the invention is to provide a system for preventing movement of the vehicle and for providing controlled movement of the boom when the personnel work platform is in use. Further, it is an object of the present invention to incorporate a shut-off switch on the personnel work platform such that the workers standing on the personnel work platform can shut down operation of the vehicle boom from the work platform. Yet another object of the invention is to provide a PWP control system that locks the stabilizing cylinder of the forklift and prevents operation of auxiliary hydraulics when the forklift is in a PWP mode of operation.
The present invention is a control system that modifies the operation of a boom-type vehicle, such as an extendible boom forklift, when the vehicle is being used in connection with a personnel work platform (PWP). The PWP control system of the present invention modifies the operation of the forklift to increase the safety of workers positioned on the work platform.
The PWP control system includes a shut-off switch that is mounted near the work platform and a PWP system actuator switch. The shut-off switch and PWP system actuator switch are interconnected with a control microprocessor included in the electronic operating circuit for the forklift. The control microprocessor is configured to selectively operate various operating components of the forklift in a PWP mode, which is different than the normal mode of operation.
The PWP system actuator switch is positioned in the cab of the forklift and must be actuated for the PWP control system to enter the PWP mode. In addition to the actuation of the PWP system actuator switch, the microprocessor must detect the simultaneous actuation of the service brakes. Specifically, the PWP system actuator switch and the service brakes must be simultaneously applied for a period of five seconds before the microprocessor allows the control system to enter the PWP mode.
Upon entering the PWP mode, the PWP control system performs several functions to further ensure the safety of a worker on the personnel work platform. Upon entering the PWP mode, the microprocessor sends a signal to the transmission controller, which causes the transmission of the forklift to declutch, to prevent movement of the forklift. At the same time, the processor activates the parking brake and locks the rear axle stabilizing system of the forklift to provide a secure four-point stance.
Once the forklift enters the PWP mode, the PWP control system checks to determine whether the cab of the forklift is in a generally level orientation. Specifically, a level sensor/switch in the cab provides a signal to the microprocessor indicating the orientation of the cab. If the sensor/switch determines that the cab is tilted one way or the other more than 2xc2x0, the microprocessor will disable operation of the forklift boom to prevent movement of the personnel work platform.
In addition to controlling various operational components of the forklift, the microprocessor causes a restriction in the flow of hydraulic fluid to the leveling cylinder of the forklift upon entering the PWP mode. The flow restriction reduces the rate at which the leveling cylinder operates to prevent a worker on the platform from being thrown from the platform due to a tip-over of the forklift caused by incorrect movement of the leveling cylinder.
The PWP control system of the invention includes the shut-off switch that is mounted to the personnel work platform. If a worker on the personnel work platform desires to prevent any further movement of the boom, the worker can depress the shut-off switch. When the shut-off switch is moved to its OFF position, the microprocessor activates a joystick disengage solenoid that prevents any further movement of the boom. Thus, a worker on the platform can prevent further movement of the platform by an operator in the forklift cab.